Impregnated dielectric materials



March 30, A w TH M ON IMPREGNATED DIELECTRIC MATERIALS AND IMPREGNATING COMPOSITIONS Filed Dec. 4, 1955 PROTECTIVE SH EATH ELECTRIC cow DUCTOR I MPR EGNATE D DIELECTRIC MATERIAL 171 De 71 to r: MM 012% Mm,

Patented Mar. 30, 1937 IMPREGNATED DIELECTRIC MATERIALS AND IMPREGNATING COMPOSITIONS Archibald Walter Thompson, Bromley, England Application December 4, 1935, Serial No. 52,885 In Great Britain December 13, 1934 13 Claims.

This invention consists in improvements in or relating to impregnated dielectric materials suitable for cable wrappings or interleaving sheets for condensers or for like purposes. An object 5 of the invention is to produce an insulating material having high resistance to oxidation and good dielectric properties.

It is customary to impregnate paper or like wrappings for electric cables with oil but difll- 10 culties arise in practice because the oil is apt to drain away from the paper or the like. Mixtures of oil and resin having a high viscosity are commonly employed to impregnate paper or like wrappings with a View to obviating draining but 15 such mixtures are susceptible to oxidation and it is found difficult to obtain sufiiciently good dielectric properties.

It has now been discovered that hydrocarbons of very high viscosity (e. g. 2000 to 3000 seconds Redwood at 200 F.) may be obtained by polymerizing suitable petroleum fractions in the presence of certain metallic chlorides, e. g. aluminium chloride.

According to this invention an impregnated dielectric material comprises paper or like absorbent fibrous material impregnated with a mixture of a highly viscous hydrocarbon, having a viscosity value between the limits 2500 and 3000 seconds Redwood at 200 F., with a less viscous mineral oil having a viscosity value less than 200 seconds Redwood at 200 F. The mixture is a homogeneous mixture of the oils and should have a viscosity value of between 1500 and 3000 seconds Redwood at 140 F. Preferably the high viscos- 35 ity hydrocarbon is refined, before mixing, by any suitable refining process, for example by treatment with selective solvents (e. g. the Duosol process) or with liquid sulphur dioxide or by acid treatment or alkali treatment or by bleaching 40 with earths or by high vacuum distillation.

In order to reduce the likelihood of gassing or cheese" formationin the dielectric material under electric stress (which commonly results when a saturated parafiinic or olefinic oil is em- 45 ployed) it is a further feature of the invention to use, as the mineral oil (which should preferably have a viscosity value between 50 and 200 seconds Redwood at 200 F), a pure, highly refined naphthenic oile. g. the Sun Oil Companys 50 XX oil. Preferably the mixture comprises 30% of said highly viscous hydrocarbon.

The invention includes an electric cable wrapped with paper or like absorbent fibrous material (e. g. jute) impregnated with the mix- 55 ture described. Preferably the impregnation is carried out during or after the wrapping steps.

In one specific example of the invention which will now be described, a high viscosity hydrocarbon was prepared by polymerizing the heavy ends from a petrol produced by cracking crude oil, in the presence of anhydrous aluminium chloride, the polymerization being carried out in the vapour phase, and to the full extent so as to give the maximum viscosity. The high viscosity product so obtained was mixed with highly refined naphthenic oil in the proportions of one part of the product to two parts of the oil. This mixture has a viscosity of 2,500 seconds Redwood at 60 C. so being in accordance with normal European practice, and was employed to impregnate a paper-wrapped electric cable.

Any suitable petroleum fraction (e. g. any frac" tion between petrol and fuel oil) may be polymerized to give the high viscosity product and the polymerization may be carried out in either the liquid or vapour phase.

It is found that a cable wrapped with paper impregnated with the mixture described has a particularly high dielectric resistance, and re sistance to oxidation as well as low power Iactor losses and that'the cable may be operated at temperatures up to 20 to C. higher than is the usual practice without causing thermal instability and subsequent breakdown. The size of the cable and consequently the cost may therefore be de 39 creased without sacrifice of safety.

The drawing is a diagrammatic representation of an electric cable provided with an insulating covering formed from a strip of absorbent fibrous material wrapped around the electric conductor and impregnated either before or during the wrapping operation with the hydrocarbon mixture hereinbefore described. The cable may be provided with the usual protective sheath of any suitable material.

The invention includes the use, as an impregnating medium for dielectric materials, of a mixture of a hydrocarbon of high viscosity and a a comparatively low viscosity mineral oil.

I claim:

1. An impregnated dielectric material comprising an absorbent fibrous material impregnated with a mixture of a highly viscous hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F., with a less viscous 59 mineral oil having a viscosity value of less than 200 seconds Redwood at 200 F.

2. An impregnated dielectric material comprising an absorbent fibrous material impregnated with a mixture of a highly viscous hydrocarbon,

having a viscosity value between 2500 and 3000 seconds Redwood at 200 F., with a less viscous mineral oil having a viscosity value between 50 and 200 seconds Redwood at 200 F., which mixture has a viscosity value between 1500 and 3000 seconds Redwood at 140 F.

3. An impregnated dielectric material comprising an absorbent fibrous material impregnated with a mixture of a highly viscous refined hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F., with a less viscous mineral oil having a viscosity value of less than 200 seconds Redwood at 200 F.

4. An impregnated dielectric material comprising an absorbent fibrous material impregnated with a mixture of a highly viscous hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F. with a highly refined naphthenic oil having a viscosity value of less than 200 seconds Redwood at 200 F.

5. An impregnated dielectric material comprising an absorbent fibrous material impregnated with a mixture of a highly viscous hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F. with a less viscous mineral oil having a viscosity value between 50 and 200 seconds Redwood at 200 F. which mixture has a viscosity value between 1500 and 3000 seconds Redwood at 140 F. said mixture containing about 30% of said highly viscous hydrocarbon.

6. An impregnated dielectric material comprising paper impregnated with a mixture of a highly viscous hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at zoo F. with a less viscous mineral oil having a viscosity value of less than 200 seconds Redwood at 200 F.

7. An impregnated dielectric material comprising paper impregnated with a mixture of a highly viscous refined hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F. with a highly refined naphthenic oil having a viscosity value between 50 and 200 seconds Redwood at 200 F. which mixture has a viscosity value between 1500 and 3000 seconds Redwood at 140 F,

8. An impregnated dielectric material comprising paper impregnated with a mixture of a highly viscous refined hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F. with a highly refined naphthenic oil having a viscosity value between and 200 seconds Redwood at 200 F. which mixture has a viscosity value between 1500 and 3000 seconds Redwood at F. said mixture containing about 30% of said highly viscous refined hydrocarbon.

9. An impregnated dielectric material for an electric conductor comprising a strip of absorbent fibrous material wrapped around said conductor and impregnated with a mixture of a highly viscous refined hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F. with a highly refined naphthenic oil having a viscosity value between 50 and 200 seconds Redwood at 200 F. which mixture has a viscosity value between 1500 and 3000 seconds Redwood at 140 F., said mixture containing about 30% of said highly viscous refined hydrocarbon.

10. An impregnating medium for dielectric materials comprising a mixture of a highly viscous hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F. with a less viscous mineral oil having a viscosity value of less than 200 seconds Redwood at 200 F.

11. An impregnating medium for dielectric materials comprising a mixture of a highly viscous hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F. with a highly refined naphthenic oil, having a viscosity value of less than 200 seconds Redwood at 200 F.

12. An impregnating medium for dielectric materials comprising a mixture of a highly viscous hydrocarbon, having a viscosity value between 2500 and 3000 seconds Redwood at 200 F. with a highly refined naphthenic oil, having a viscosity value between 50 and 200 seconds Redwood at 200 F. said mixture containing about 30% of said highly viscous hydrocarbon and having a viscosity value between 1500 and 3000 seconds Redwood at 140 F.

13. An impregnated dielectric material comprising an absorbent fibrous material impregnated with a mixture of a highly viscous hydrocarbon, having a viscosity value between 1500 and 3000 seconds Redwood at 200 F., with a less viscous mineral oil having a viscosity value of less than 200 seconds Redwood at 200 F.

ARCI-IIBALD WALTER THOMPSON. 

